Annulus filler system

ABSTRACT

An annulus filler system bridges the gap between two adjacent blades attached to a rim of the rotor disc of a gas turbine engine. The system includes an annulus filler having a lid which extends between the adjacent blades and defines an airflow surface for air being drawn through the engine. The filler also has a support body extending beneath the lid and terminating in an elongate foot which, in use, extends along a groove provided in the rim of the disc. The groove has a neck which prevents withdrawal of the foot through the neck in a radially outward direction of the disc. The system further includes a sleeve which, after installation of the filler, is slidably locatable into a gap between the foot and sides of the groove.

FIELD OF THE INVENTION

The present invention relates to an annulus filler system for bridgingthe gap between adjacent blades of a gas turbine engine stage.

BACKGROUND OF THE INVENTION

With reference to FIG. 1, a ducted fan gas turbine engine generallyindicated at 10 has a principal and rotational axis X-X. The enginecomprises, in axial flow series, an air intake 11, a propulsive fan 12,an intermediate pressure compressor 13, a high-pressure compressor 14,combustion equipment 15, a high-pressure turbine 16, and intermediatepressure turbine 17, a low-pressure turbine 18 and a core engine exhaustnozzle 19. A nacelle 21 generally surrounds the engine 10 and definesthe intake 11, a bypass duct 22 and a bypass exhaust nozzle 23.

The gas turbine engine 10 works in a conventional manner so that airentering the intake 11 is accelerated by the fan 12 to produce two airflows: a first air flow A into the intermediate pressure compressor 13and a second air flow B which passes through the bypass duct 22 toprovide propulsive thrust. The intermediate pressure compressor 13compresses the air flow A directed into it before delivering that air tothe high pressure compressor 14 where further compression takes place.

The compressed air exhausted from the high-pressure compressor 14 isdirected into the combustion equipment 15 where it is mixed with fueland the mixture combusted. The resultant hot combustion products thenexpand through, and thereby drive the high, intermediate andlow-pressure turbines 16, 17, 18 before being exhausted through thenozzle 19 to provide additional propulsive thrust. The high,intermediate and low-pressure turbines respectively drive the high andintermediate pressure compressors 14, 13 and the fan 12 by suitableinterconnecting shafts.

Conventionally, a compressor rotor stage comprises a plurality ofradially extending blades mounted on a disc. The blades are mounted onthe disc by inserting a root portion of the blade in a complementaryretention groove in the outer face of the disc periphery. To ensure aradially smooth inner surface for air to flow over as it passes throughthe stage, annulus fillers can be used to bridge the spaces betweenadjacent blades. Typically, a seal between the annulus fillers and theadjacent fan blades is also provided by resilient strips bonded to theannulus fillers adjacent the fan blades.

Annulus fillers of this type are commonly used in the fan stage. Thefillers may be manufactured from relatively lightweight materials and,in the event of damage, may be replaced independently of the blades

It is known to provide annulus fillers with features for removablyattaching them to the rotor disc. An annulus filler may be provided witha hook member at its axially rear end, the hook member sliding intoengagement with part of the rotor disc and/or a component locatedaxially behind the rotor assembly, for example a rear fan air seal.Typically, such an annulus filler is slid axially backwards over therotor disc following an arc which matches the chord-wise curvatures ofthe aerofoil surfaces of the adjacent blades until the hook memberengages, and is then retained in place by a front attachment disc whichis fastened over the fronts of all the annulus fillers located aroundthe rotor disc.

U.S. Pat. No. 4,655,687 proposes an annulus filler that can be fitted tothe rotor disc in a radial direction of the disc. The annulus fillerthat has a salient foot that is shaped similarly to re-entrant groovesformed in the disc rim between pairs of adjacent blades. The foot isproportioned so as to pass radially of the disc through the neck of arespective groove. Wedges positioned between opposing walls of thegrooves and respective feet then prevent withdrawal of the feet in adirection radially outwardly of the disc.

U.S. Pat. No. 6,132,175 proposes a compliant sleeve for ceramic turbineblades that addresses irregularities between the ceramic blade dovetailand the disc. The sleeve also acts as a compliant member to reducefrettage.

SUMMARY OF THE INVENTION

An aim of the present invention is to provide annulus fillers that aresuitable for use with composite blades, and in particular carbon fibrereinforced plastic (CFRP) blades. As such blades are lighter than metalblades and as the casing containment system for the blades in the eventof a blade off event also tends to be lighter, it is desirable that thefiller is lightweight to increase engine efficiency and to reduce theenergy of impact on the containment system and blades if parts of theannulus filler should be released.

Accordingly, a first aspect of the present invention provides an annulusfiller system for bridging the gap between two adjacent blades attachedto a rim of the rotor disc of a gas turbine engine, the systemincluding:

-   -   an annulus filler having a lid which extends between the        adjacent blades and defines an airflow surface for air being        drawn through the engine, and a support body extending beneath        the lid and terminating in an elongate foot which, in use,        extends along a groove provided in the rim of the disc, the        groove having a neck which prevents withdrawal of the foot        through the neck in a radially outward direction of the disc,        and    -   a sleeve which, after installation of the filler, is slidably        locatable into a gap between the foot and sides of the groove;    -   wherein the foot is formed of composite material and the sleeve        provides a galvanic isolation layer preventing galvanic        corrosion between the foot and the disc.

Thus the composite material foot (and typically other composite materialparts) of the filler can reduce the filler mass. However, as galvaniccorrosion can be a problem between composite materials, particularlythose containing carbon fibres, and metals, the sleeve enables a fillerhaving at least a composite material foot to be used with, for example,a metal disc by preventing galvanic corrosion between the foot and thedisc. The sleeve can also provide a suitable interface between arelatively soft filler foot and a relatively hard disc.

The annulus filler system may have any one or, to the extent that theyare compatible, any combination of the following optional features.

Typically, the disc is a metal disc.

Typically, the foot is formed of fibre-reinforced plastic, e.g.carbon-fibre reinforced plastic. Galvanic corrosion can be a particularproblem between carbon fibres and metals.

Conveniently, the foot may be proportioned to pass through the neck ofthe groove in a radial direction on installation of the filler. Thesleeve can then be proportioned to prevent withdrawal of the footthrough the neck, after installation of the filler, in a radiallyoutward direction of the disc.

Typically, the groove extends in substantially an axial direction of theengine, i.e. substantially aligned with retention slots in the disc rimfor retaining the blades. The groove may follow a straight or a curvedpath from the front to the rear of the disc. The walls of the groove maybe parallel, or the groove may taper from one end to another.

The sleeve may have a stop which engages with the rim to prevent thesleeve from sliding beyond its intended location position.

Typically, the sleeve wraps around the foot to extend from one side ofthe neck to the other. Indeed, the sleeve may be configured to protrudepast the neck of the groove and to flare outwardly away from the supportbody. In this way, free edges of the sleeve outside the groove can bekept away from the support body of the annulus filler, avoiding damageto the support body from those edges.

The annulus filler may further have sealing strips along the edges ofthe lid to seal to the adjacent blades.

The sleeve may have a layer of ballotinis within the galvanic isolationlayer. The ballotinis can ensure a minimum thickness for the galvanicisolation layer. For example, the layer of ballotinis may be at theinner surface of the sleeve and contact, in use, the foot. Theballotinis, which can be formed e.g. of glass or resin, are generallyeffective galvanic isolators and can reliably space the foot from otherparts of the sleeve which offer less galvanic corrosion protection. Theballotinis may be completely or partially embedded in a matrix such as alayer of resin or an adhesive. For example, with partial embedding, aportion of each ballotini may be proud of the matrix such that only theballotinis and not the matrix contact the foot. This can help to improvethe galvanic isolation of the foot by reducing the foot surface area incontact with the sleeve.

Alternatively a galvanic isolation layer can be provided by: a layer ofglass fibre in a non-conductive matrix; a glass layer formed or fusedonto the surface of the sleeve; or a paint layer or coating. Whichevertype of layer is adopted, it should be resilient to direct loading, forexample from forced rocking of the annulus filler by the blades, or fromforeign objects impacting the airflow surface of the lid of the filler.

The sleeve may be bonded to the foot after the sleeve is located in thegap, e.g. by a resin or adhesive. For example, a cyno-acrylic adhesivemay be applied to the inner surface of the sleeve before location of thesleeve. The adhesive then cures after location of the sleeve in thepresence of water to bond the sleeve to the foot. Such adhesives arerelatively strong in tension, helping the sleeve to remain in locationin use, but relatively weak in shear, allowing the sleeve to be removedfor servicing, inspection or maintenance. Conveniently, the ballotinismay be embedded in the resin or adhesive, such as a paste adhesive. Apaste adhesive (e.g. a nitrile phenolic adhesive, or a two partcatalytic set epoxy adhesive such as 3M Scotch-Weld 2216™ or a thermosetepoxy adhesive such as 3M Scotch-Weld AF500™), whether used with orwithout ballotinis, can advantageously act as a damper between the footand the sleeve. It can also act as a filler to accommodate manufacturingtolerances between the foot and the sleeve, and can help to excludemoisture from the interface between the foot and the sleeve.

The foot may have an outer layer of glass fibre, e.g. woven or braidedglass fibre. Such a layer can also improve the galvanic isolation of thefoot.

The sleeve may have an anti-frettage coating at its outer surface, theanti-frettage coating contacting, in use, the disc. For example, theanti-frettage coating may be formed of molybdenum disulphide, tungstendisulphide or polytetrafluoroethylene. The anti-frettage coating may beselectively located at positions on the outer surface most susceptibleto fretting. The anti-frettage coating may be applied e.g. by thermalspraying, PVD or ebPVD, as appropriate.

The sleeve may have a main body, for example with the galvanic isolationlayer on an inner surface of the body and/or an anti-frettage coating onits outer surface. The main body can be metallic. For example, it can beformed from a conventional titanium alloy, or a high damping alloy suchas a titanium-niobium alloy or a titanium-hafnium alloy of the typeknown as gum metal. A damping alloy can help to resist shear motion atthe sleeve-disc interface and hence to reduce fretting. Other metallicor non-metallic materials can be used to form the main body of thesleeve depending on, loading, and filler foot interaction required.

Typically, the foot has a dovetail-shaped cross-section. The groove canbe correspondingly dovetail-shaped in cross-section. Alternatively,however, the foot may have a circular cross-section, e.g. on a stalkextending from the support body.

Preferably, the lid is formed from fibre-reinforced plastic, e.g. CFRP.

The support body may have a pair of side walls, each side wall joining arespective edge of the lid to the foot to give the support body aV-shaped cross-section. As the V-shaped cross-section supports the lidat its edges, the edges of the lid are less likely to disintegrateduring an extreme event. Preferably, the side walls are formed fromfibre-reinforced plastic, e.g. CFRP. Preferably a cavity formed by thelid and the two side walls contains a foam core, e.g. formed from aplastic material such as a foamed resin or syntactic foam. The foam corecan provide a stiffer filler structure, more able to retain its shape.Alternatively, however, the cavity may contain a chopped fibrecomposite, e.g. a chopped carbon fibre in a resin such as epoxy.

An annulus filler in which the lid, support body and foot are all formedof composite or plastic material can be made very lightweight, helpingto increase the efficiency of the engine.

A second aspect of the present invention provides a sleeve of theannulus filler system according to the first aspect.

A third aspect of the present invention provides a rotor assemblyaccording to the first aspect.

A fourth aspect of the present invention provides a rotor assembly for agas turbine engine including:

-   -   a rotor disc,    -   a plurality of blades attached to a rim of the disc of a gas        turbine engine, and annulus filler systems according to the        first aspect bridging the gaps between adjacent blades;    -   wherein respective grooves are provided in the rim, the feet of        the annulus fillers extending along the grooves, and the sleeves        being located in the gaps between the feet and the sides of the        grooves.

Preferably, the rotor disc is a fan disc. The blades may be formed ofcomposite material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described by way of examplewith reference to the accompanying drawings in which:

FIG. 1 shows a longitudinal section through a ducted fan gas turbineengine;

FIG. 2 shows schematically a perspective view of an annulus filler of anembodiment of the present invention;

FIG. 3 shows schematically a perspective view of a retention sleeve ofthe embodiment;

FIG. 4 shows schematically an end on view of the annulus filler and theretention sleeve of the embodiment when fitted to a groove of a rotordisc;

FIG. 5 shows schematically a side view of the fitted annulus filler andretention sleeve;

FIG. 6 shows schematically a transverse cross-section through theretention sleeve of FIGS. 3 to 5; and

FIG. 7 shows schematically a transverse cross-section through anotherembodiment of a retention sleeve.

DETAILED DESCRIPTION

FIGS. 2 and 3 show schematically perspective views of respectively anannulus filler 30 and a retention sleeve 35 of an annulus filler systemaccording to an embodiment of the present invention. The filler has alid 31 which, in use, extends between two adjacent composite fan blades,and a support body 32 extending beneath the lid and terminating in anelongate foot 33. The support body is formed by two side walls 34 whichjoin to the lid along respective edges of the lid and meet at the footto give the body a V-shaped cross-section. The foot has a dovetailcross-section, e.g. with about 55° flank angles. The retention sleeve 35is shaped to wrap around the foot 33.

FIG. 4 shows schematically an end on view of the annulus filler 30 andthe retention sleeve 35 when fitted to a groove 36 of a metal rotordisc, and FIG. 5 shows schematically a side view on the engine axialline of the fitted filler and sleeve. The groove is dovetail-shaped incross-section, like the foot 33, and is located on the disc rim in theoutside face of post 38 formed between slots 39 which hold the fanblades 40 to the disc. An alternative arrangement has a circular footcross-section and a correspondingly circular groove cross-section. Thegroove may follow a straight or a curved path from the front to the rearof the disc, and the sleeve is correspondingly straight or curved. Toinstall the annulus filler system into the groove, the annulus filler ispositioned outwardly of the groove and then moved radially inwardly. Thewidest part of the foot is proportioned to pass through the neck 41 ofthe groove so that the foot can be located completely in the groove.This enables fitting annulus fillers between blades that are shaped suchthat the fillers cannot be slid into position along the groove in agenerally rearward direction of the engine. To prevent withdrawal of theannulus filler in a radially outward direction, the retention sleeve 35is slidingly located into the gap formed between the groove and thefoot. The sleeve wraps around the foot and protrudes past the neck ofthe groove to flare outwardly away from the support body so that thefree edges 42 of the sleeve are kept away from the support body 32. Thishelps to prevent the free edges from damaging the support body or posts38 if there is relative movement between the sleeve and the body.

A stop 43 at the end of the sleeve 35 prevents the sleeve from slidingin one direction out of the groove 36. Sliding of the sleeve in theother direction can be prevented by a support ring 44 fitted to the faceof the disc 37 after location of the sleeve. Thus together the stop andsupport ring can ensure repeatable axial positioning and retention ofthe sleeve.

When fitted, the lid 31 of the annulus filler 30 forms a continuousairflow surface along with a nose cone 45 at the front of the lid and aseal ring 46 at the rear of the lid. Sealing strips 47 extending alongthe edges of the lid seal the lid to the sides of the adjacent blades40.

Advantageously, the foot 33 and groove 36 retention system candistribute loads over the entire axial length of the filler 30. Thisallows the use of a lightweight filler which can improve engineefficiency. The weight of the filler can be reduced, for example, byforming the lid 31, the side walls 34 and the foot 33 from carbon fibrereinforced plastic.

The lid may be secured to the side walls by stitching through laminatelayers, which can help to stiffen the edges of the lid, therebyproviding a secure base for the sealing strips 47. The cavity formed bythe lid and side walls can be filled with a foam core 48 or have aninternal lattice structure, which can provide a lightweight resilientsupport to the lid and side walls. Such support can absorb impact energyand help the lid and side walls to retain their shape after impactdeformation. The filler may be produced by foaming the material of thecore within a pre-preg envelope of the lid, side walls and foot, andthen completing the lid, side walls and foot by resin transfer moulding.

More specifically, the basic filler structure can be formed as apre-preg tube by 3D Braiding or 3D weaving carbon fibres. An outer layerof glass fibre, e.g. woven or braided glass fibre can be applied to thefoot to improve the galvanic isolation of the foot. A former can beplaced inside the preform, which is then resin transfer moulded. Thefoam core is foamed in situ in the cavity and the surfaces sealed. Thelid may have a coating, such as an elastomer (e.g. polyurethane),applied to resist sand, debris, and tool drops. Typically the coatingwould be applied as a sheet or sprayed on. A more sophisticated 3Dbraided or woven structure can be made to provide internal struts orlattice within the cavity, in which case more than one former may berequired during moulding.

FIG. 6 shows schematically a transverse cross-section through the sleeve35. The inner surface of the sleeve is covered with a layer ofballotinis 48. The ballontinis are partially or fully embedded in alayer of resin or adhesive 49 such that the ballotinis ensure a minimumthickness for the galvanic isolation layer formed by the ballotinis andthe resin. The galvanic isolation layer isolates the carbon fibres inthe foot from the rest of the sleeve and the metal disc 37. If theballotinis are partially embedded in the resin, only the proud portionsof the ballotinis may make contact, in use, with the foot 33. This canreduce the contact area of the foot with the sleeve. However, a pasteadhesive may be used to fill the gaps between the ballotinis and providea loose bond to the filler foot. Such a paste adhesive is preferablychosen to provide damping to the filler foot.

Two sizes of ballotinis may be used: the larger size being onlypartially embedded and having proud portions penetrating to an extentinto the surface of the foot and thereby improving the locking betweenthe foot and the sleeve, and the smaller size being fully embedded withthe resin or paste adhesive to ensure a minimum thickness for thegalvanic isolation layer.

The sleeve has a main body 50 which carries the layer of ballotinis 48on its inner surface. The main body can be formed, for example, of aconventional titanium alloy, or a high damping alloy such as atitanium-niobium-oxygen alloy or a titanium-hafnium-oxygen alloy.Advantageously, a damping alloy can help to resist shear motion at thesleeve-disc interface and hence to reduce fretting.

The outer surface of the main body 50 may be treated with ananti-frettage coating 51, such as molybdenum disulphide, tungstendisulphide or polytetrafluoroethylene. The coating may be applied onlywhere needed rather than over the entire outer surface. The coating maybe a sprayed on or applied by PVD/ebPVD.

FIG. 7 shows schematically a transverse cross-section through anotherembodiment of the sleeve 35. The sleeve is formed with various layers.The main body 52 is preferably metallic and may, for example, be analloy of titanium, or a high damping titanium alloy such as Ti₃(Ta, Nb,V)+(Zr, Hf, O) (known as gum metal). The outer surface of the main bodycarries an anti-fretting coating 53. The inner surface of the main bodycarries a galvanic isolation layer 54 formed, for example, by a layer ofglass fibre in a non-conductive matrix.

While the invention has been described in conjunction with the exemplaryembodiments described above, many equivalent modifications andvariations will be apparent to those skilled in the art when given thisdisclosure. For example, the filler may be slid into position along thegroove in a generally rearward direction of the engine, i.e. the sleevemay not need to prevent withdrawal of the annulus filler in a radiallyoutward direction. Accordingly, the exemplary embodiments of theinvention set forth above are considered to be illustrative and notlimiting.

All references referred to above are hereby incorporated by reference.

1. An annulus filler system bridging the gap between two adjacent bladesattached to a rim of the rotor disc of a gas turbine engine, the systemincluding: an annulus filler having a lid which extends between theadjacent blades and defines an airflow surface for air being drawnthrough the engine, and a support body extending beneath the lid andterminating in an elongate foot which, in use, extends along a grooveprovided in the rim of the disc, the groove having a neck which preventswithdrawal of the foot through the neck in a radially outward directionof the disc, and a sleeve which, after installation of the filler, isslidably locatable into a gap between the foot and sides of the groove;wherein the foot is formed of composite material and the sleeve providesa galvanic isolation layer preventing galvanic corrosion between thefoot and the disc.
 2. An annulus filler system according to claim 1,wherein the composite material comprises carbon fibres.
 3. An annulusfiller system according to claim 1, wherein the galvanic isolation layeris selected from the group consisting of: a layer of glass fibre in anon-conductive matrix; a glass layer formed or fused onto the surface ofthe sleeve; and a paint layer or coating.
 4. An annulus filler systemaccording to claim 1, wherein the sleeve has a layer of ballotiniswithin the galvanic isolation layer.
 5. An annulus filler according toclaim 3, wherein the sleeve has a layer of ballotinis within thegalvanic isolation layer.
 6. An annulus filler system according to claim4, wherein the layer of ballotinis are at the inner surface of thesleeve and contact, in use, the foot.
 7. An annulus filler systemaccording to claim 4, wherein the ballotinis are embedded in an adhesiveor resin.
 8. An annulus filler system according to claim 1, wherein thesleeve has an anti-frettage coating at its outer surface, theanti-frettage coating contacting, in use, the disc.
 9. An annulus fillersystem according to claim 1, wherein the sleeve has a metallic main bodywith the galvanic isolation layer on the inner surface of the sleeve.10. An annulus filler system according to claim 1, wherein the lid isformed from fibre-reinforced plastic.
 11. An annulus filler systembridging the gap between two adjacent blades attached to a rim of therotor disc of a gas turbine engine, the system including: an annulusfiller having a lid which extends between the adjacent blades anddefines an airflow surface for air being drawn through the engine, and asupport body extending beneath the lid and terminating in an elongatefoot which, in use, extends along a groove provided in the rim of thedisc, the groove having a neck which prevents withdrawal of the footthrough the neck in a radially outward direction of the disc, and asleeve which, after installation of the filler, is slidably locatableinto a gap between the foot and sides of the groove; wherein the foot isformed of composite material and the sleeve provides a galvanicisolation layer preventing galvanic corrosion between the foot and thedisc, wherein the composite material comprises carbon fibres; whereinthe galvanic isolation layer is selected from the group comprising: alayer of glass fibre in a non-conductive matrix; a glass layer formed orfused onto the surface of the sleeve; or a paint layer or coating. 12.An annulus filler system according to claim 11, wherein the sleeve has alayer of ballotinis within the galvanic isolation layer.
 13. An annulusfiller system according to claim 12, wherein the layer of ballotinis areat the inner surface of the sleeve and contact, in use, the foot.
 14. Anannulus filler system according to claim 12, wherein the ballotinis areembedded in an adhesive or resin.
 15. An annulus filler system accordingto claim 11, wherein the sleeve has an anti-frettage coating at itsouter surface, the anti-frettage coating contacting, in use, the disc.16. An annulus filler system according to claim 11, wherein the sleevehas a metallic main body with the galvanic isolation layer on the innersurface of the sleeve.
 17. A rotor assembly for a gas turbine engineincluding: a rotor disc, a plurality of blades attached to a rim of thedisc of a gas turbine engine, and annulus filler systems according toclaim 1 bridging the gaps between adjacent blades; wherein respectivegrooves are provided in the rim, the feet of the annulus fillersextending along the grooves, and the sleeves being located in the gapsbetween the feet and the sides of the grooves.
 18. A rotor assembly fora gas turbine engine including: a rotor disc, a plurality of bladesattached to a rim of the disc of a gas turbine engine, and annulusfiller systems according to claim 11 bridging the gaps between adjacentblades; wherein respective grooves are provided in the rim, the feet ofthe annulus fillers extending along the grooves, and the sleeves beinglocated in the gaps between the feet and the sides of the grooves.